Combined depth gauge and pneumatic analogue decompression instrument

ABSTRACT

In this computer for calculating and indicating safe minimumduration decompression schedules, a porous body serves the double purpose of supporting the gas diffusion membrane and providing a substantially constant gas chamber. Additionally, the immersible housing of the instrument has an integrally-formed depth gauge in the form of an arcuate rib portion having a tapered axial bore open only at its larger end. A single instrument dial serves both the computer gauge and the depth gauge in this coordinated assembly.

11] 3,759,101 14 1 *Sept..18, 19 73 1 1 COMBINED DEPTH GAUGE AND 5/1926Coberly.........

PNEUMATIC ANALOGUE DECOMPRESSION INSTRUMENT [75] Inventors: Marcus P.Borom; Lyman A. primary s Clement Swisher Attorney-John F. Ahern et a1.

Johnson, both of Schenectady, N.Y.

General Electric Company, Schenectady, N.Y.

[73] Assignee:

[57] ABSTRACT In this computer for calculating and indicating safeminimum-duration decompression schedules, a porous Hofihe tefirTof thepatent s *1 rhepoa'is body serves the double purpose of supporting thegas diffusion membrane and providing a substantially constant gaschamber. Additionally, the immersible housing of the instrument has anintegrally-formed depth gauge in the form of an arcuate rib portionhaving a tapered axial bore open only at its larger end. A singleinstrument dial serves both the computer gauge and the depth gauge inthis coordinated assembly.

Sept. 16, 1971 211 App]. No.: 181,096

[52] US. 73/291, 73/432 R, 235/184 [51] Int. (:01: 23/14, G06g 5/00 [58]Field of Search....'.............; 73/432 R, 299, 300,

6 Claims, 3 Drawing Figures References Cited UNITED STATES PATENTSCOMBINED DEPTH GAUGE AND PNEUMATIC ANALOGUE DECOMPRESSION INSTRUMENT Thepresent invention relates generally to the art of computingdecompression schedules and is more particularly concerned with a novelpneumatic analogue decompression instrument which continuously sensesambient pressures experienced during hyperbaric exposure and computesand indicates a minimumduration safe decompression schedule.

CROSS REFERENCES This invention is related to those of the followingfour patent applications assigned to the assignee hereof and filed ofeven date herewith:

US. Pat. application Ser. No. 181,048, filed Sept. 16, 1971, entitled,Pneumatic Analogue Decompression Instrument," in the name of Marcus P.Borom, which discloses and claims the concept of using a permselectivemembrane to simulate the gas-diffusion characteristics of body tissuesas they take up the gas of the breathing mixture and release it asambient pressure varies.

US. Pat. application Ser. No. 181,107, filed Sept. 16, 1971, entitled,Multi-Time Constant Pneumatic Analogue Decompression Instruments," inthe names of Lyman A. Johnson and Marcus P. Borom, which discloses andclaims the concept of matching different time-constants of various bodytissues with membrane chambers of different diffusion controlledtimeconstant characteristics to provide a versatile decompression meter.

U.S. Pat. application Ser. No. 181,099, filed Sept. 16, 1971, entitled,Single Gauge Multi-Time Constant and Multi-Tissue Ratio AutomaticDecompression lnstruments, in the names of Marcus P. Borom and Lyman A.Johnson, which discloses and claims the concept of connecting severaldifferent time-constant membrane assemblies in an automatic switchingrelation with a single gauge so that the gauge always indicates thehighest pressure prevailing anywhere in the system.

US. Pat. application Ser. No. 181,106, filed Sept. 16, 1971, entitled,Miniaturized Automatic Decompression Meters, in the names of Marcus P.Borom and Lyman A. Johnson, which discloses and claims the combinationof a constant-volume gas chamber and a liquid-filled gauge which enablesminiaturization without impairing performance of the instrument.

BACKGROUND OF THE INVENTION The major hazard faced by both commercialand sport divers is decompression sickness which results from therelease of dissolved gases from the body tissues as discrete bubbleswhen the ambient pressure is reduced too rapidly. As the ambientpressure is increased during a dive, the body tissues begin to absorbmore gas from the breathing mixture to equilibrate with this pressurechange. The rate of such equilibration varies from tissue to tissue, butnot significantly from person to person, nor between compression anddecompression phases, and is vitally important only in the course ofreturn from hyperbaric exposure. Also, the tissues can withstand, tovarying degrees, an internal over-pressure (i.e., supersaturation)during decompression without nucleating gas bubbles. This is referred toas a tissue ratio and is given by the expression Tissue ratio Safemaximum tissue pressure/ambient pressure with the pressures given on anabsolute scale. The rate of descent, therefore, is a matter of thedivers choice while the rate of ascent is limited by a combination ofthe tissue ratio and the rate at which the dissolved gases enter thebloodstream in the dissolved state and are removed from the body throughthe lungs.

Boycott, Damant and Haldane [The Prevention of Compressed-Air Illness,J. Hygiene, 8, 342-443 (1908)] proposed that the body tissues can beconsidered to be gas-diffusion chambers arranged in a parallel circuitwith each chamber having a characteristic tissue half time and tissueratio.

On the basis of their model, Boycott, et al. proposed a radicaldeparture from the conventional continuous decompression schedules whichbecame known as stage decompression. Today their model forms the basisfor the modern decompression schedules as set forth in the Standard NavyDecompression Tables. These Tables have been computed using tissue halftimes of 20, 40, and minutes and tissue ratios from 2.5/1 to 1.8/1.These Tables are designed for fixed mission dives, that is, dives to apredetermined depth for a predetermined time. Consequently, they are notsuitable for the majority of commercial and sport dives since theyprescribe a longer-than-necessary decompression schedule as thealternative to hazarding an estimate compensating for depth excursionsduring a dive.

Recognizing the need for a better answer to the problem, the prior artprovided decompression meters having input, computation and read-outcomponents of various kinds. in these devices, however, computation isaccomplished by the resistive flow of a gas through an orifice or aporous medium which follows the mathematics of Poiseuille flow and notdiffusion through a membrane. These devices, then, share thecharacteristic of inability to compute minimum-duration safedecompression schedules according to the Boycott, et al. model. Thus,because of Poiseuille flow, tissue gas uptake and release actions arenot computed according to the expression used in developing the accepteddecompression tables. The use of a diffusion membrane provides theprecise analogue to these expressions.

SUMMARY OF THE INVENTION The decompression meter of this invention makesdouble use of one element of structure of the versatile instruments ofthe aforementioned related patent applications. Additionally, itincorporates in accordance with the novel concept hereof in oneinstrument both the decompression schedule computing and indicatingmeans with the depth gauge which is coordinated for read-out on the samedial. The double-use concept and the coordinated double-gauge featureafford net substantial advantages over the instruments heretofore knownof this kind and at the same time they do not in any way limit utilityor operation of the instrument or otherwise incur or involve substantialoffsetting penalty or disadvantage.

DESCRIPTION OF THE DRAWINGS The novel features and advantages of theinstruments of this invention will be more clearly apparent from thedetailed description set forth below taken in conjunction with thedrawings accompanying and forming a part of this specification, inwhich:

FIG. 1 is a vertical sectional view of an instrument embodying thisinvention in a preferred form;

FIG. 2 is an enlarged, vertical sectional view of the body portion ofthe instrument of FIG. 1 showing the ambient-pressure sensing computingmeans and elements ofthe indicator means in assembled, operativerelation; and

FIG. 3 is a sectional view of the instrument of FIG. 1 taken on line 3-3thereof to illustrate the coordinated relationship between the capillarydepth gauge tube and the instrument dial.

DESCRIPTION OF THE INVENTION I Self-contained instrument of FIGS. 1 and2 is enclosed in a housing 12 comprising a cover 13 in the form of aflanged cup-like body and a bottom plate 14 secured to cover 13 by bolts15 through the flange of cover 13. The cover and bottom plate are madeof transparent plastic having the physical strength to withstand thepressures encountered at diving depths. Plate 14 has a threaded axialaperture 17 providing access to instrument compartment 18 in thehousing.

Instrument 10 includes an L-shaped metal body 20 and gauge assembly 22supported by conduit 23 secured to body 20 which is supported within thehousing by threaded engagement at its lower end 24 with bottom plate114. An enlarged axial bore is provided in the lower end of body 2t) toreceive components of the ambient pressure-sensing means, the computingmeans and the indicator means of instrument W, and threads 25 areprovided within the lower open end of the body. A bore 27 of reduceddiameter connects the inner end of the enlarged bore cavity with theupper end of body 20 where it communicates with conduit 23.

Bourdon, tube 23 of gauge assembly 22 communicates with bore 27 throughconduit 23 and as indicated in the drawings, the volume thus provided isliquidfilled. The bourdon tube is connected to indicator 31 andinstrument dial 32 so that when pressure of liquid within tube 29 ischanged, indicator 3B is caused to move relative to dial 32 and therebyshow the pressure change on the dial.

The liquid within bourdon tube 29, conduit 23 and bore 27 is sealedagainst leakage into the enlarged bore portion of body 20 by diaphragm35 of natural rubber. Diaphragm 35 is held in place by disc 37 whichincludes a metal ring 38 and a porous ceramic cylinder 39 which fillsthe space within the ring and provides the volume serving as thetime-constant chamber of the computing means.

Ambient-pressure gas chamber $0 of this instrument is provided by metalcylinder 42 and a rubber diaphragm 43 which closes the lower open end ofcylinder 42 and is held in place by washer 44 and compression nut 45.Cylinder 42 has a central portion through which a small diameteraperture 47 opens into a recess in the top of the cylinder in which aporous ceramic disc 48 is disposed. A silicone rubber membrane 50 ofabout lO-mils thickness is disposed between the upper surface ofcylinder 32 and disc 48 and the opposed lower surfaces of ring 38 andceramic cylinder 39. Thus, diffusion membrane 50 is supported againstgas pressure differentials by the fritted glass or other suitable porousceramic of cylinder 39 and disc 48 and at the same time is effective todiffuse gas species in either direction between ambient-pressure gaschamber 40 and timeconstant chamber 39.

As disclosed in copending US. Pat. application Docket No. RD-3993, thedevice of this invention may be provided in the form of the FIG. 3instrument of that case for use in the breathing gas supply line of thediver instead of being self-sufficient. The reconstruction andmodification of the device of FIGS. 1 and 2 hereof can suitably besubstantially as shown and described in US. Pat. application Docket No.RD-3993, rubber diaphragm 43 being replaced suitably by a disc which isnot deformed under conditions of intended use, and appropriateconnection being made between the diver's breathing gas supply line (notshown) and ambientpressure gas chamber 40.

It will also be understood by those skilled in the art that theparticular membrane used for the gas-diffusion function of theinstrument may be of material other than silicone rubber, the criteriafor selection of alternative membrane materials being those set forth inthe specification of copending US. Pat. application Docket No. RD-3993,the disclosure of which is incorporated herein by reference.

A capillary depth gauge 55 is provided in the form of a capillary borein the upper portion of cover 13. The capillary bore opens through port56 to the outside of cover 13 and is tapered over its length from port56 to bulb 57 at its closed end, the length-diameter relationshipenabling direct read-out of water depth in feet on dial 32. Housing 10,consequently, is positioned relative to dial 32 so that bulb 55 islocated just beyond the 50-foot mark and aperture 56 is at the dial zeroposition.

MODE OF OPERATION The mode of operation of the instruments of thisinvention generally resembles that of the copending US. Pat. applicationDocket No. RD-3993. Thus, as the volume of ambient-pressure gas chamber40 fluctuates with changes in the water pressure applied to diaphragm43, gas pressure in chamber 40 varies and influences the diffusion ofgas through membrane 50. Pressure increase in chamber 40 resulting ingas diffusion into chamber 39 is shown on dial 32 as indicator 31 isactuated in response to displacement by diaphragm 35 of the liquid inbore 27 and bourdon tube 23. Likewise, a decrease in the pressure of gasin chamber 40 results in gas diffusion from chamber 39 through membrane50 and a corresponding reduction in pressure shown by the gauge asdiaphragm 35 returns to or toward the rest position illustrated by FIG.2.

It will be understood in regard to FIG. 3 that the zero depth point ondial 32 represents 15 pounds-persquare-inch pressure. Consequently,before underwater use of considerable time after the instrument has beenremoved from the water following a dive, indicator 31 will rest againstpeg P representing possibly only a few pounds gauge pressure, i.e., 15to 18 pounds absolute pressure. Then, as the instrument is subjected tohyperbaric pressure underwater, indicator 31 moves up the dial scaleindicating the take-up of nitrogen or other gas (depending upon thespecies of the breathing gas mixture in chamber 40) by body tissue asrepresented by diffusion membrane 50. At the same time, water flowsthrough port 56 into capillary bore 55, compressing air in the capillaryin proportion to the water pressure at the depth of the instrument.After a considerable period during which diffusion of gas throughmembrane 50 results in movement of indicator 3i to the position outlinedin FIG. 3, the depth gauge may likewise indicate a depth of 13 feet.Variations of readings between indicator 31 and the depth gauge 5 will,however, normally occur during the large part of a diving period. Forexample, if a diver proceeds directly to a depth of about 50 feet fromthe surface, the capillary depth gauge will immediately register thatdepth against dial 32 but indicator 31 will at first not move off peg Pand then later will move comparatively slowly up the scale until itreaches the depth at which the diver begins his decompression scheduleof ascent to the surface. In this instance, the diver at 50 feetobserving indicator 31 in the outlined position of FIG. 3, knows that hemay safely proceed directly to the 13- foot depth level without adecompression stop. He then can approach the surface as the indicatormoves toward the zero point on the scale, or he may proceed stepwisewith one or more stops on the way up. The latter procedure will usuallybe preferred, however, when the initial decompression stop shown by theFIG. 3 instrument is at the -foot or deeper level.

The letter indicia on dial 32 (FIG. 3) correspond to the lettersemployed in the Standard Navy Decompression Tables for use incalculating the requirements of decompression'and breathing gas supplyfor repetitive dive situations. In other words, after the diver hasreturned to the surface via a decompression schedule, indicator 31 movesfrom the zero position in the direction of peg P and points to one afteranother of the letter indicia, thus enabling the diver to determinequickly, before re-entry into the water, the letter" condition of hisbody tissues which-is related to the pressure of the residual absorbedgas in the tissues. Reference to the Standard Navy Decompression Tablesfor repetitive dives then permits the diver to make a critical allowancefor such residual gas pressure in the tissue, particularly from thestandpoint of scheduling the duration of the impending dive against thebreathing 40 gas supply available to him.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

I. A decompression instrument which comprises,

a. ambient pressure-sensing means including an ambient-pressurc gaschamber;

b. computing means for measuring continuously uptake and release of gasby human tissues under fluctuating hyperbaric ambient pressuresincluding 1. a porous body providing a substantially constant volume gaschamber,

2. a gas-diffusion membrane supported by the porous body and disposedbetween and separating the ambient-pressure gas chamber and the constantvolume gas chamber; and,

c. indicator means including a gauge operatively associated with thecomputing means for indicating the appropriate decompression schedule interms of hyperbaric pressures and time intervals.

2. The instrument of claim 1 including a second porous body disposed onthe ambient-pressure gas chamber side of the gas-duffusion membrane andproviding support for said gas-diffusion membrane.

3. The instrument of claim 1 in which the porous body is of ceramicmaterial.

4. The instrument of claim 2 in which both porous bodies are of ceramicmaterial.

5. In a decompression instrument, in combination,

a. ambient pressure-sensing means including an ambient-pressure gaschamber;

b. computing means for measuring continuously uptake and release of gasby human tissues under fluctuating hyperbaric ambient pressures;

c. indicator means including 1. a dial bearing indicia of water depthsand repetitive dive groups of diving tables,

2. a guage operatively associated with the computing means having anindicator for registry with the dial to show the appropriatedecompression schedule of stop depths and times and the inert gas debtin body tissues influencing repetitive dives, and

3. a capillary tube depth gauge coordinated with the dial for read-out.

6. The instrument of claim 5 including a housing having a transparentportion and a rib portion formed in the housing and containing thecapillary tube depth gauge with its open end opposite the zero point ofthe linear scale of water depth.

1. A decompression instrument which comprises, a. ambientpressure-sensing means including an ambient-pressure gas chamber; b.computing means for measuring continuously uptake and release of gas byhuman tissues under fluctuating hyperbaric ambient pressuresincluding
 1. a porous body providing a substantially constant volume gaschamber,
 2. a gas-diffusion membrane supported by the porous body anddisposed between and separating the ambient-pressure gas chamber and theconstant volume gas chamber; and, c. indicator means including a gaugeoperatively associated with the computing means for indicating theappropriate decompression schedule in terms of hyperbaric pressures andtime intervals.
 2. a gas-diffusion membrane supported by the porous bodyand disposed between and separating the ambient-pressure gas chamber andthe constant volume gas chamber; and, c. indicator means including agauge operatively associated with the computing means for indicating theappropriate decompression schedule in terms of hyperbaric pressures andtime intervals.
 2. The instrument of claim 1 including a second porousbody disposed on the ambient-pressure gas chamber side of thegas-duffusion membrane and providing support for said gas-diffusionmembrane.
 2. a guage operatively associated with the computing meanshaving an indicator for registry with the dial to show the appropriatedecompression schedule of stop depths and times and the inert gas debtin body tissues influencing repetitive dives, and
 3. a capillary tubedepth gauge coordinated with the dial for read-out.
 3. The instrument ofclaim 1 in which the porous body is of ceramic material.
 4. Theinstrument of claim 2 in which both porous bodies are of ceramicmaterial.
 5. In a decompression instrument, in combination, a. ambientpressure-sensing means including an ambient-pressure gas chamber; b.computing means for measuring continuously uptake and release of gas byhuman tissues under fluctuating hyperbaric ambient pressures; c.indicator means including
 6. The instrument of claim 5 including ahousing having a transparent portion and a rib portion formed in thehousing and containing the capillary tube depth gauge with its open endopposite the zero point of the linear scale of water depth.